Sumatran Orangutan

Sumatran Orangutan

Geographical Range

Sumatra (in the South Pacific)

Habitat

Tropical forests

Scientific Name

Pongo abelii

Conservation Status

Critically endangered

Confined to the Trees

Orangutans are arboreal, meaning they live the majority of their life high up in the trees of their tropical rainforest habitat. This tree-living lifestyle is where the species received their name. “Orangutan,” of Malaysian origin means “person of the forest.” It is a fitting name for this aps so well adapted to a life in the trees that is essentially has four hands (their feet are just like hands) to climb through the canopy of the forest. The orangutan rarely leaves the trees, even making nests in the branches of the trees to sleep in at night or nap in during the day.

Note: There are two distinct species of orangutans: the Bornean orangutan, Pongo pygmaeus, and the Sumatran orangutan, Pongo abelii. The latter is the one you can see at the Saint Louis Zoo. Although their habits are almost identical, the two species live on separate islands in the South Pacific.

Big Red

Orangutans’ unique bright red hair makes these large apes easy to recognize. But the two sexes are also easy to distinguish from one another. Male orangutans are about twice the size of females, weighing up to 300 pounds and reaching a height of five feet. Not only are the males much larger, but they also develop a throat pouch and prominent cheek pads when sexually mature, about 15 years old.

Thanks to some pretty distinctive physical adaptations, orangutans are the only apes that live primarily in trees. (While chimpanzees, bonobos and western lowland gorillas can climb and nest in trees, they spend most of their lives on the ground.) orangutans’ feet are so well adapted for grasping tree branches, for instance, that they cannot place them flat on the ground. Instead, they have to walk on the outside of the curved foot (called "fist-walking").

In addition, they have extremely long arms for reaching, slender hands with short thumbs and long fingers for hooking over branches, and flexible hips for holding on in any direction. Plus, orangutans have tremendous strength. This enables them to swing from branch to branch and to hang upside-down for long periods of time to retrieve food.

These traits make it possible for orangutans to perform almost all of their necessary behaviors while suspended in the trees – including feeding, traveling, mating, nesting and child rearing. However, these apes move so awkwardly on the ground that they’re essentially unable to live anywhere else but in the forest canopy.

A Passion for Fruit

By far the favorite food of wild orangutans is fruit and it usually makes up about 60% of their diet. They have been observed eating more than 300 kinds of fruit, the two most common of which are figs and durian. When fruit is unavailable, they also eat leaves, stems, tree bark, and insects such as ants and termites.

Knowing what kinds of food to eat and not to eat is not a simple matter in tropical forests. Orangutans need to know hundreds of species of plants and trees, which fruits are edible, and how to get at tasty food that’s covered by sharp spines or shells. Babies rely on their mothers to teach them these skills, as well as where to find food, in which trees, and during which seasons. A successful orangutan is thought to have a very detailed mental “map” of the forest in his or her mind, including knowledge of the fruiting cycles of many species of trees.

Because trees produce fruit only seasonally, this food source tends to be irregular and widely distributed. Although orangutans have an uncanny ability to remember from year to year which trees fruit and when, they’re still limited by the patchy supply (and their slow speed). That means foraging is highly competitive, and any one area can’t support many orangutans. Hence the reason these apes are solitary.

Stocking the Toolbox

Many wild orangutans have developed an amazing ability to use tools to help them exploit what food they can find. They’ve been observed using probes like twigs to extract insects and honey from tree trunks (held in their hands or their teeth), as well as blunt tools to scrape seeds from spiny fruit cases.

In addition to food-gathering tools, wild orangutans have been observed making tools to scratch themselves, fashioning leafy branches into “umbrellas” to shelter themselves from sun and rain, and using branches as swatters to repel bees or wasps that are attacking. Many have also been seen using “leaf gloves” to handle prickly fruits or branches, or creating “seat cushions” to sit comfortably in thorny trees.

Tool use hasn’t been observed in all orangutan populations, and it shows great variations even when it exists. This suggests to scientists that tool use is the result of innovation and learning that’s passed on from one generation to the next – one of the hallmarks of culture.

A Long Childhood

Except for humans, orangutans have the longest childhood of any animal in the world. Babies of more social ape species can learn from multiple adults, orangutan babies depend on just one adult -- their mother. Female orangutans usually mature around 12 or 13 years, giving birth around the age of 15. The mother orangutan will carry her baby around with her for the first year. Around two or three years old, the baby orangutan will start to stray form the mother, but never more than a few feet away and will return to the mother often. For the next several years, the orangutan baby will learn from its mother how to find food, make a nest, and use tools. Once the mother orangutan has a new baby, the young orangutan will start to learn to live apart from its mother, although returning frequently.

Orangutans have one of the longest periods of time between births of any terrestrial mammal, with female orangutans having a baby approximately every nine years and the pregnancy lasting approximately eight months and twenty days. This low reproductive rate of orangutans is another limiting factor in their survival in the wild.

Baby orangutans nurse until they are about six years of age, slowly learning how to eat fruit and other solid food as they travel through the forest with their mother. Even after weaning, a young male often stays close by his mother for a few more years. Eventually, males become usually nomadic, often traveling great distances from their home region. "Long-calls" and loud roars enable them to maintain their distance from one another in the forest.

Young females, however, may stay near their mother until they are into their teens. This allows them to observe parenting skills as they watch their mother care for a younger sibling. Males are not successful in attracting sexually receptive females until they get their cheek pads, also as teenagers.

Orangutans normally live about 35 to 40 years in the wild; in captivity they’ve been known to live into their 50s.

A Solitary Life

Wild orangutans generally live alone (see A Passion for Fruit above), a byproduct of their food preferences. The only long-term bond they have is between a female and her young. When orangutans do encounter one another, they are normally very tolerant and non-aggressive, unless the encounter is between two mature males.

A male in control of a home range that includes several females often won't tolerate the intrusion of other males. Fights occasionally break out. One male usually charges another, breaking branches and threatening his rival. If that doesn’t scare him off, the two might grapple and bite each other until one backs down.

A Species on the Brink

About 10,000 years ago, orangutans were found throughout Southeast Asia, even in southern China. Scientists estimate there were probably hundreds of thousands of orangutans. Today, however, only 10,000-25,000 still survive in the tropical forests of Borneo and Sumatra.

Both Bornean and Sumatran orangutans have been in dire trouble for some time. The primary reasons are habitat loss and degradation from logging, forest fires, and timber clearing for farming (including palm oil plantations) and human settlements. orangutans are also hunted and killed for their meat (bushmeat), and young apes are captured for sale in the illegal pet trade.

Sumatran orangutans could be extinct in the wild in as little as five years.

To the Rescue

So what can be done to help Sumatran orangutans? Though the situation is dire, there are organizations and individuals in many countries trying to reverse their severe decline. They are working to stop illegal logging, to increase sustainable economic alternatives for communities surrounding orangutan habitat, helping instill national pride in orangutans and their environment, and rehabilitating ex-captive orangutans into protected habitat. To find out about one such group -- the Balikpapan Orangutan Society -- click on www.orangutan.com.

You can help too. You can donate money to conservation organizations working to help orangutans or to save their habitat. You can also help in the effort to protect orangutan habitat by choosing wisely when you shop for certain products. Avoid buying wood or wood products that originate in fragile tropical forest areas:

Ramin is one of the most frequently logged types of wood from Borneo – used to make broom and brush handles and other common consumer items. To avoid ramin, instead choose items with plastic or metal handles.

Teak, ironwood, ebony and sandalwood are all logged in Indonesia. Avoid these.

The unsustainable harvest of lauan, a tropical plywood, is taking a huge toll on tropical forest habitat in Asia and the South Pacific. Make sure any plywood you buy (including plywood used in flooring and furniture construction) is harvested sustainably. Certain retailers, including Lowe’s and Home Depot, are taking steps to discontinue sale of lumber products from environmentally sensitive areas. Ask your retailer where your wood products come from.

The production of rayon, made from wood pulp, is a huge consumer of rainforest resources. Avoid buying clothes made with rayon viscose.

Palm oil plantations have been responsible for the clearing of hundreds of thousands of acres of orangutan habitat.

Fun Facts:

In the Malay language, the name "orangutan hutan" means "person of the forest.”

Early indigenous people of Indonesia and Malaysia wouldn’t kill an orangutan because they felt it was simply a person hiding in the trees, avoiding work.

Although orangutans don’t use a lot of vocalizations, one sound they do make is a “kiss squeak,” often used when they’re alarmed or displeased.

Baby Orangutan

The Zoo is Helping Sumatran Orangutans

North American zoos, including the Saint Louis Zoo, are working together to ensure the future of captive orangutans. We participate in the Species Survival Plan® (SSP) for Sumatran orangutans. This is a cooperative breeding program, with a number of zoos working together to ensure the survival of the species.

Cell Phone Recycling

With a simple donation of your cell phone, you can help animals and the environment. The St. Louis chapter of American Association of Zoo Keepers will collect unwanted cell phones and cell phone accessories at the Zoo and earn funds for conservation efforts around the world.

Cell phones can be donated at the Welcome Desk at the North and South Entrances, 9 a.m. - 5 p.m. daily, or mailed to Saint Louis Zoo, One Government Drive, St. Louis, MO 63110.

The Trouble with Palm Oil

Orangutans are in trouble in the wild. Their forest homes are being destroyed to make way for palm oil plantations. Palm oil plantations are responsible for the clearing of hundreds of thousands of acres of orangutan habitat. Learn more about palm oil, its effect on orangutans, and how you can help.